Stress concentration factors in joints of square hollow section (SHS) brace and concrete-filled SHS chord under axial tension in brace

It has been shown that concrete filling of square hollow section (SHS) chords in trusses increases fatigue life at the joint between the chord and the SHS brace. Nonetheless, currently there are no expressions for the stress concentration factor (SCF) at these joints. In this study, a robust finite element investigation is carried out to examine SCF in 90° joints made up of empty SHS braces and concrete-filled SHS (CFSHS) chords under axial tension in the brace. Results were validated against experimental data. A comprehensive parametric study was then carried out on 80 FE models to generate a large database for SCFs, considering the effects of key non-dimensional parameters, namely; width ratio between brace and chord of 0.4-1.0, width to wall thickness ratio of the chord of 12.5-25, and wall thickness ratio between brace and chord of 0.25-1.0. Using multiple regression analyses, a series of formulae for SCF were developed for practical design applications. A comparison of SCFs in joints with hollow and concrete filled chords shows a 10-26% reduction in SCFs in concrete-filled chords, leading to better fatigue behavior.